Multi-holed orifice vs single (central) hole, all else equal

[frogcurry]

Question: Does a multi-hole orifice have any difference to a single hole orifice in terms of behaviour (other than the reduced noise levels?). I am thinking in terms of increased downstream turbulence as the two or more flows recombine, changes in the balance of flow, etc causing increased pressure loss overall. The flow area of the two items would be identical.

My initial thinking was the flow would have higher pressure drop, and so some consideration was needed, but I am starting to think otherwise, as all the action in orifices essentially happens at the hole. Opinions of this board would be appreciated.

 

[khan101]

You can use two approaches in this manner with probably same results. One is to assume that all holes will act together as one hole so you add the area of all holes and count them as one larger hole. Two, you can assume that each hole will act as an individual orifice and will not be affected by other holes. You can calculate flow for one hole and then multiply them by the number of holes.
Rosemount manufactures multi-hole orifice plate as a standard product, look for Rosemount 1595 conditioning orifice plate.

 

[MikeHalloran]

Two small distant orifices in a powerdam could not interact to a measurable degree.

Two small orifices in a pipe or a valve body must interact.

All the action does not happen at the hole. On the upstream side, the isobars around the hole(s) are hemispheres. The flow is radially spherically inward.

Symmetry does not apply, else we would have evolved differently.

On the downstream side, the flow leaving the hole stays in a stream, that slows and grows wider as it loses energy to the surrounding fluid. That initially quiescent fluid on the downstream side of the orifice(s) is induced to flow toroidally. The flow near the downstream face of the orifice plate is radially inward toward the orifice(s), just as on the upstream face. The isobars are not hemispherical, but more complex.

The geometry in both upstream and downstream chambers/ pipes affects the flow fields upstream and downstream, unless the chambers/ pipes are semi- infinite relative to the orifice diameter.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA